The present invention relates to an improvement in the body fluid absorbent articles such as sanitary napkins used to absorb and thereby to hold menstrual discharge.
Body fluid absorbent articles such as sanitary napkins of prior art generally comprise a surface structure composed of a topsheet molded from thermoplastic film formed with liquid passages or channels spaced from one another in longitudinal, transverse and diagonal directions of the topsheet, each of these liquid passages or channels being opened at both upper and lower ends thereof, and an absorbent core of which the top surface is covered with the topsheet. Such surface structure can be basically classified into three types as will be described below.
One example of the first type is disclosed in Japanese Patent Application Publication No. 1982-17081. A topsheet constituting a surface structure in this patent application is molded from thermoplastic film so that a plurality of liquid passages tapered downward and their lower openings are close in contact with the top surface of an absorbent core. With such arrangement, however, if each liquid passage is tapered downward as extremely as almost to a critical diametric dimension of its lower opening beyond which a quantity of body fluid once absorbed by the absorbent core may partially flow backward again the lower openings of the liquid passages, the lower openings of the liquid passages may be blocked by a clot, assumed that the body fluid is menstrual discharge containing such clot, and no additional discharge can be smoothly transferred into the absorbent core. If the lower openings of the liquid passages are dimensioned so as to avoid this problem, the quantity of menstrual discharge having been absorbed in the absorbent core will be visible for users in a vivid shade and users may feel uncomfortable when she disposes used napkin. With the topsheet made from light-transmissive plastic film such as polyethylene film, the quantity of menstrual discharge having been absorbed in the absorbent core will be visible for users in a relatively light shade through ribs defining the upper openings of the respective liquid passages.
Another example of the first type is disclosed in Japanese Patent Application Disclosure Gazette No. 1989-249502. A topsheet forming a surface structure disclosed therein comprises a thermoplastic film layer laminated on the bottom surface of a thermoplastic fibrous layer. Since this topsheet is of two-layered structure composed of a fibrous layer and a plastic film layer, it never takes place that the quantity of menstrual discharge having been absorbed in an absorbent core is visible for users in a lighter shade through the topsheet. While this topsheet is preferred to the previously mentioned topsheet so far as the shielding effect for menstrual discharge is concerned, there remains the problem that the quantity of menstrual discharge having been absorbed in the absorbent core is visible for users in a relatively vivid shade through openings of the respective liquid passages.
One example of the second type is disclosed in Japanese Patent Application Disclosure Gazettes Nos. 1986-158954; 1989-119251; and 1990-19153. A topsheet forming a surface structure disclosed therein is molded from hydrophobic plastic film formed with liquid channels having bottoms closed and side walls opened. With such surface structure, the quantity of menstrual discharge having been absorbed in an absorbent core is not visible for users through the liquid channels. However, the closed bottoms of the respective liquid channels function as barriers preventing a sufficient quantity of menstrual discharge from being rapidly transferred to the absorbent core and clots of menstrual discharge, if any, will be apt to cling to the bottoms and stay there, resulting in that these clots are sometimes visible for users in a vivid shade.
One example of the third type is disclosed in Japanese Patent Application isclosure Gazette No. 1982-89861. A topsheet forming a surface structure disclosed therein comprises a hydrophobic meshy topsheet, a hydrophobic fibrous layer disposed on the bottom surface of said hydrophobic meshy topsheet, and a hydrophobic plastic film layer formed with tapered liquid passages and disposed on the bottom surface of said fibrous layer. This surface structure is normally effective to avoid the problem that the quantity of menstrual discharge having been absorbed in an absorbent core is visible for users through the liquid passages. However, clots of menstrual discharge, if any, may cling to fibres of the meshy topsheet as well as of the underlying fibrous layer and block the meshes, preventing a sufficient quantity of menstrual discharge from smoothly flowing into the liquid passages. In such case, menstrual discharge may be vividly visible for users just as with the above-mentioned second type of surface structure.
In view of such problems, it is a principal object of the invention to provide a surface structure for the article as mentioned in the beginning so improved that, in spite of using a topsheet formed with a plurality of liquid passages, an adequate quantity of menstrual discharge can be rapidly transferred to an absorbent core and the quantity of menstrual discharge having been absorbed in the absorbent core are substantially invisible for users.